Such methods and likewise the associated apparatus for carrying out the method are known in particular from dry sweeping machines, in which the sweepings, and in particular the portion of fine dusts in the sweepings are not absorbed by water during the sweeping. Instead, the fine dust is separated in the dust collector on filter elements, after the coarse sweepings have previously settled, under the action of gravity and with the cooperation of an impingement hood, in the receptacle for coarse sweepings.
The problem underlying the present invention consists in that the fine dusts accumulated in the dust collector of a dry sweeping machine are liable to penetrate the lungs due their particle size and, possibly, contain health damaging substances, and that they cannot be easily added in untreated form to the receptacle for coarse sweepings. Moreover, because of the suction air current within the receptacle for coarse sweepings, it is problematic to return the fine dusts in the form of dust to the receptacle for coarse sweepings. This would lead to an endless maintenance or concentration of the dust circulation.
The present invention is based on the further development of the method described in DE 4 94 211 and the apparatus disclosed therein for a gastight discharge of the dust separated in the collection chamber of gas-cleaning installations by its removal therefrom. The further development of this known method from the year 1930 has become necessary due to the fact that the compressing of the dust into an open pipe does not permit a continuous process and, thus, is unsuitable for cleaning the dust filter of a dry sweeping machine, as is described below in more detail with reference to FIG. 1.
Shown in FIG. 1 is a compression tube 8 with a plug 18 (dust in compressed form) and with a compression chamber 12 filled with dust. Assuming a hydrostatic state of stress and a Coulomb state of friction on the tube wall, the mathematical model for the compacted mass being formed results in an exponential increase of pressure in direction toward a piston ram 17 with an exponent of 4 .mu.l : D, where .mu. is the coefficient of friction, 1 the length of the compression tube or the compression chamber, and D the diameter of the compression tube. In a continuous compacting process with an alternating piston ram 17, a new compact is produced in compression chamber 12, the plug 18 is pushed up, and the compact is moved to this position. This means that the plug 18 is brought from the state of static friction to the state of sliding friction. Since the coefficient of static friction is always greater than the coefficient of sliding friction, the compacted mass is further compressed during each stroke of the piston ram due the exponential increase in pressure. After few strokes of piston ram 17, this results in that the plug 18 is no longer pushed out. A conceivable shortening of the length 1 of plug 18 itself would result in that the gas contained in the fluidized bed of dust diffuses into the plug 18, destroys the compressed structure and, thus, allows the compacts to become softer and softer. Thus, the known method as well as the known apparatus are unsuitable for a continuous operation.